New 3D-printed bottle caps tell us when our milk has gone bad

When making a bowl of cereal or a cup of tea, many of us have exactly the same reflex; we sniff the milk. Perfectly sensible, you don’t want to ruin your morning with sour dairy—but no one really wants a nose full of stinky milk either. A new 3D-printed bottle cap that detects bacteria could save us from nasal distress while reducing both food waste and sickness.

Developed by engineers from UC Berkeley and Taiwan’s National Chiao Tung University, the smart bottle cap uses regular 3D-printing technology to embed liquid metal pastes within the plastic piece. These metal pastes can produce basic microelectric components—in the case of the bacteria-sniffing bottle cap, a “wirelessly readable inductor–capacitor (LC)-resonant circuit.”

As detailed in the team’s paper, recently published in the journal Nature, this electrical circuit can in turn detect changes in levels of bacteria in the milk—all one has to do is tip the bottle upside down to ensure the liquid comes into contact with the resonant circuit. No sniffing required, happy nose, edible cereal, and no hesitant confusion if you have a cold. And the cap isn’t just applicable to milk—it could be used in a wide variety of liquid and potentially solid foods to determine whether or not it is safe for consumption.

The new cap could even alert store owners and consumers that food is reaching the end of its edible state—doing away with vague and wasteful “best before” and “use by dates.” In a statement from UC Berkeley, the project’s lead author Liwei Lin explained: “This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers… You could imagine a scenario where you can use your cellphone to check the freshness of food while it’s still on the store shelves.”